HR: 1330h
AN: S22A-0414    [PDF]
TI: Earthquake Locations, Depths and Source Parameters From the Himalayan Nepal Tibet Seismic Experiment (HIMNT): Implications for Continental Lithospheric Strength.
AU: * Monsalve, G
EM: monsalve@colorado.edu
AF: University of Colorado, University of Colorado at Boulder CB 399, Boulder, CO 80309 United States
AU: Sheehan, A
EM: afs@cires.colorado.edu
AF: University of Colorado, University of Colorado at Boulder CB 399, Boulder, CO 80309 United States
AU: Wu, F
EM: wu@binghamton.edu
AF: SUNY Binghamton, SUNY Binghamton P.O. Box 6000, Binghamton, NY 13902 United States
AU: De La Torre, T
EM: tomd@lithos.colorado.edu
AF: University of Colorado, University of Colorado at Boulder CB 399, Boulder, CO 80309 United States
AU: Blume, F
AF: University of Colorado, University of Colorado at Boulder CB 399, Boulder, CO 80309 United States
AU: Huang, G
AF: SUNY Binghamton, SUNY Binghamton P.O. Box 6000, Binghamton, NY 13902 United States
AU: Sapkota, S
AF: National Seismological Centre, National Seismological Centre, Department of Mines and Geology, Lainchour, Kathmandu, NPL Nepal
AU: Rajaure, S
AF: National Seismological Centre, National Seismological Centre, Department of Mines and Geology, Lainchour, Kathmandu, NPL Nepal
AB: The Himalayan Nepal Tibet Seismic Experiment (HIMNT) included the deployment of 29 broadband IRIS PASSCAL seismometers in eastern Nepal and southern Tibet from October 2001 to November 2002. An initial catalog with hundreds of local earthquakes has been obtained by picking the first arrivals of P and S waves and locating the hypocenters using a weighted least squares algorithm. We find a dense alignment of seismic events along the front of the High Himalaya, following the general trend of the surface trace of the Main Central Thrust. Many earthquakes cluster at 15-25 km depth along the proposed mid-crustal ramp beneath the High Himalaya of northern Nepal, where interseismic accumulation is believed to take place. Earthquakes with depths between 70 and 85 km are found in northeastern Nepal and southern Tibet. The Sub-Himalaya of southern Nepal is almost free of seismicity, with the exception of a cluster of earthquakes in the vicinity of the 1988 magnitude 6.1 Udaypur earthquake. Many of these southern Nepal earthquakes are at depths very close to the crust-mantle boundary. A double difference algorithm has been utilized in order to relocate earthquakes, improving the ability of the seismicity pattern to image the active tectonic structures. Phase picks from 21 short period seismic stations of Department of Mines and Geology of Nepal (DMG) are combined with HIMNT picks in the relocations. After relocation, the alignment of earthquakes following the front of the High Himalaya becomes more clear, as well as the clustering of hypocenters along the inferred mid-crustal ramp. The alignment of the aftershocks of the Udaypur earthquake likely mark the fault plane along which the strike-slip motion occurred. Estimates of local crustal thickness from teleseismic receiver functions combined with hypocenter locations indicate an upper mantle origin for many earthquakes in southern Tibet and northeastern Nepal, which has important implications for the strength of the continental lithosphere. A full waveform moment tensor inversion is performed for the largest events, obtaining further constrain on earthquake depth as well as the mechanisms of faulting in the area.
DE: 7205 Continental crust (1242)
DE: 7215 Earthquake parameters
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2003 Fall Meeting